The present invention relates to a new and improved construction of a thread tensioning apparatus for use with a warp creel, especially in warp and beam warping installations. The present invention also relates to a warp creel, especially in warp and beam warping installations, and which is equipped with the new and improved construction of the thread tensioning apparatus.
In its more particular aspects the present invention specifically relates to a new and improved tensioning apparatus for use in a warp creel, especially in warp and beam warping installations, and which contains a pair of brake plates, one of which is mounted for rotation and in an axially stationary manner. An other one of the brake plates is peripherally centered at the rotationally driven brake plate. The other brake plate can be pressed against the rotationally driven brake plate with a variable and adjustable pressure by means of a tensioning device which acts upon the center of the other brake plate. The tensioning device comprises a compression spring, one end of which is supported at a gripping sleeve which is slideable along a pressing pin surrounded by the compression spring. The gripping sleeve is operatively connected to a displaceable control plate which extends parallel to the pressing pin and by means of which there can be simultaneously varied the pressure applied by a predetermined number of such similar tensioning devices.
A thread tensioning apparatus of the type as described hereinbefore is known, for example, from Swiss Pat. No. 636,653 and permits, in addition to a total displacement of all tensioning devices of a creel by displacing the control plate, an individual adjustment of each individual tensioning device in order to compensate for differences in the tension of the individual threads. Such differences in the thread tensions may be due to different thread runs between bobbins or spools which are placed at a starting position and at an end position of the creel, between bobbins or spools in horizontal and vertical rows and others. The known tensioning device is very easily serviceable because it can be mounted and dismounted by means of a few manual manipulations. Particularly, the entire tensioning device can be removed and re-mounted without any tools since the gripping sleeve is chucked by means of a clamping piece or member.
It is, however, a disadvantage of this known thread tensioning apparatus that even when the compression spring is totally relieved and when the control plate is displaced through its maximum displacement, the thread which is drawn between the two brake plates is still braked due to the inherent weight of the tensioning device and that of the other or top brake plate. In order to diminish this disadvantage and also in order to operate at the smallest possible thread tensions, it is required in the known thread tensioning apparatus to design the other or top brake plates and the members which act thereupon, even in the totally relieved state of the thread tensioning apparatus due to their inherent weight, with the lowest possible weight. It will be understod that there is thus impaired the strength and the service life of such members and that also greater expenses are caused thereby.
For this reason there are known quite a number of thread tensioning apparatuses which permit by-passing a force accumulator which generates the basic tension, by employing measures which counteract the force accumulator in order to thereby enable a completely tension-free passage of the thread between the two brake plates.
In a thread brake as known, for example, from Swiss Pat. No. 577,571 or German Gebrauchsmuster No. 7,400,404, the other or top brake plate is loaded by means of a spring or by means of weights and can be lifted off from the one or base brake plate by means of a ram which extends through a gap in the one or base brake plate and acts upon the other or top brake plate. The stroke of the ram required therefore is generated by means of an eccentric disc.
In a similar arrangement as known, for example, from German Pat. No. 597,635, German Pat. No. 975,270 as well as U.S. Pat. No. 2,912,185, the pressure generated by a helical spring is gradually reduced by means of a lever linkage. In a thread tensioning apparatus as known, for example, from Swiss Pat. No. 559,143, the spring relief is pneumatically effected.
The thread tensioning apparatuses as known from the last-mentioned printed publications have the common disadvantage that the clamping region between the brake plates is traversed by members of the loading and relieving means, whereby dirt and contaminant accumulations and undesired friction locations are formed. The removal of dirt or contaminants as well as the threading-in of the thread or the like is thereby rendered more difficult. In all these known thread tensioning apparatuses the loading means and the relieving means are arranged on opposite sides of the pair of brake plates. The load or relief is effected by different means such as, for example, a weight and a spring, a spring and a pneumatically operated membrane, a spring and a linkage, and thereby any fine tuning, if possible at all, is considerably impeded.
In a plate brake mechanism for wire spooling frames as known, for example, from European Patent Publication No. 11,826, the brake plates are each arranged at an end of a related hinged arm. The pressing power can be regulated by means of a compression spring which compresses the hinged arms. A second weaker compression spring acts upon the two hinged arms in such a manner as to urge the hinged arms away from each other. This second compression spring serves as a relief spring. This relief spring cannot be regulated and serves the single purpose of compensating for the masses which have to be moved. The relief spring is not at all suited for the regulation of very fine thread tensions. The entire mechanism, due to its weight and structural size or volume, is unsuited for use in combination with a warp creel.